How could this happen?

It's a question that people often ask after a tragedy. In the aftershock of the explosion at the Silver Eagle oil refinery in Woods Cross of Nov. 4 that damaged 100 homes, it's a particularly galling one.

Investigators from the U.S. Chemical Safety Board say it is a miracle that no one was killed or seriously injured in the explosion, which dislodged one nearby home from its foundation and severely damaged others. Refinery workers and a passing FrontRunner train escaped literally by minutes.

The board released its preliminary findings a couple of weeks ago. The lead investigator, Don Holmstrom, said that the program that monitors the mechanical integrity of the Silver Eagle plant had serious deficiencies. His boss, CSB chairman John Bresland, wondered out loud "how a refinery could be operating -- 17 years after the federal government enacted process safety regulations -- without an established and effective mechanical integrity program."

Utahns should be asking the same thing. Surely Silver Eagle has some explaining to do. So do regulators.

The CSB, by the way, is not a regulatory agency. It is an independent federal agency that investigates major chemical accidents at industrial sites.

So we want to know where Utah Occupational Safety and Health and the Utah Labor Commission were. They are supposed to be the compliance watchdogs for worker safety.

This is not an idle question. The CSB currently is conducting eight investigations of oil refineries in the United States. Three of those investigations are in the Salt Lake City area.

You may recall that a separate fire at Silver Eagle early this year injured four workers. The CSB also is investigating a fireball that ignited at the Tesoro refinery in Salt Lake City in October.

In the case of the Silver Eagle explosion, a 10-inch pipe carrying hydrogen gas failed, and a nearby ignition source caused the resulting cloud of gas to explode. Inspectors under contract to Silver Eagle had estimated the thickness of that pipe to be nearly one-half inch, but after the explosion it was measured at only one-eight of an inch. At the time of the failure, the hydrogen in the pipe was heated to 800 degrees Fahrenheit at a pressure of 630 pounds per square inch.

According to CSB, refinery managers have acknowledged that minimum thickness values for piping and equipment throughout the plant were miscalculated. These thicknesses help to determine when equipment must be retired due to potential failure.

How could this happen?